Filtration devices have been used in the past for the separation of components of a fluid based on the size, shape or physical character of the components and by employing hydraulic pressure. One component of the fluid (permeate or filtrate) is selectively forced through a membrane to separate that component from the remainder of the mixture. In straight-through filtration, the fluid is passed through a filter and suspended matter remains on the filter surface or within the filter matrix allowing only the filtrate to pass through. Cross-flow filtration allows for tangential flow across the filter surface to sweep away suspended matter which is unable to pass through the filter surface pores.
Ultrafiltration is typically carried out using a cross-flow filtration technique which involves a porous substrate. During cross-flow filtration, the feed flows parallel to the membrane and the permeate flows perpendicular to the membrane. One way in which this is achieved is by using a porous ceramic tube which is multi-channeled and has a high surface area for filtration. Such devices usually employ filtrate conduits to carry the filtrate to a filtrate collection zone. However, many of these configurations are bulky, and often require extensive and complicated piping arrangements.
Hoover et al. (U.S. Pat. No. 4,069,157) provided a ceramic support having a multiplicity of parallel passageways therethrough. The passageways were coated with an ultrafiltration membrane. The support had a specific surface area to volume ratio of about from 300 to 2000 m .sup.2 /m.sup.3 (3 to 20 cm .sup.2 /cm.sup.3) and a defined permeability factor which is greater than about 1.0.times.10.sup.-4 m. The general configuration of the support element is an elongated form having a constant cross-sectional shape along its length.
The passageways can be of any shape convenient for the methods of preparation and membrane insertion and the channels generally have a total cross-sectional area which comprises from about 40 to 75% of the total cross-sectional area of the element. This system requires that pressure be controlled according to the discharge of the concentrated feed stock through a valve, the flow of fresh feed stock through a pump and the flux of filtrate from an element.
Goldsmith (U.S. Pat. No. 4,781,831) disclosed a cross-flow filtration device which includes a structure of porous material which defines a plurality of passage-ways extending longitudinally from the feed end of the structure to the retentate end. A number of filtrate conduits are within the structure for carrying the filtrate from within the structure toward a filtrate collection zone. The filtrate conduits provide paths of lower flow resistance than that of alternative flow paths through the porous material. The structure is constructed such that the filtrate conduits are distributed among the passageways to provide low pressure drop flow paths for the filtrate flow from the passageways through the porous material to nearby filtrate conduits.
Thompson (U.S. Pat. No. 4,253,962) discloses a non-destructive ultrasonic vibratory system for removing the fouling layer which forms on the filter surface and reduces the filtering efficiency with use. Also disclosed is the introduction of a frequency sweep to avoid formation of sustained standing waves which are deleterious to the filter membrane.
An object of the present invention is to provide a fluid separation module which acts as a cross-flow filter capable of extracting the retentate from one portion of the module and continuously extracting the permeate (filtrate) from another portion of the module.
Another object of the present invention is to provide a fluid separation module which has a high volume specific surface area ranging from about 2 to 20 cm.sup.2 /cm.sup.3.
Another object of the present invention is to provide a fluid separation module which optimizes the transmembrane pressure such that it is uniform from the feed inlet to the retentate outlet.
Another object of the present invention is to provide a fluid separation module which is easy to fabricate and low in manufacturing cost.
Another object of the present invention is to provide a process for fluid separation which utilizes the fluid separation module.
Another object of the present invention is to provide a process which uses ultrasonic vibration to remove fouling of the passages.